This invention relates to an improvement in a non-magnetic substrate material for use in depositing crystalline or non-crystalline magnetic metallic films of Fe-Ni, Fe-Al-Si, etc.-based alloys.
In the production of, for example, film-form magnetic heads, integrated circuit elements, etc., a process has been used, which comprises applying a smooth surface finishing to a non-magnetic substrate material such as barium titanate, calcium titanate, alumina, zinc ferrite, glass or the like, washing the non-magnetic substrate material in an organic solvent such as trichloroethylene, acetone or the like, forming a magnetic metallic film of Fe-Ni or Fe-Al-Si-based alloy on the non-magnetic substrate material to a film thickness of a few to several tens .mu.m by a well known physical vapor-deposition technique such as vacuum vapor deposition, sputtering, ion plating, etc., and then heat-treating the substrate in vacuum at 500.degree.-700.degree. C. to improve the magnetic properties.
However, this conventional process has problems such as peeling of the magnetic metallic film during the heat treatment. Most conventional substrate materials have considerably different thermal expansion coefficients (.alpha.) than that of the magnetic metallic film. Thus the vapor-deposited magnetic metallic film is liable to peel off during the heat treatment for improving the magnetic properties. When a glass with a thermal expansion coefficient approximating to that of a magnetic metallic film is used as a substrate material peeling of the vapor-deposited film is less of a problem. Glass, however, is not always completely compatible with the vapor-deposited film, and thus there is still a problem in bonding strength. In addition, when a film form magnetic head is made from a glass substrate, the substrate wears by attrition caused by sliding between the head and a magnetic tape due to a low hardness of glass.
Thus, it has been desired to develop a non-magnetic substrate material having a thermal expansion coefficient approximating to that of a magnetic metallic film of Fe-Ni, Fe-Al-Si, etc. based alloys (.alpha..sub.T =120-150.times.10.sup.-7 /.degree.C.) and a hardness approximating that of magnetic powder contained in magnetic tapes (H.sub.v =500-700 Kg/mm.sup.2).